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Development of a Targeted Mass-Spectrometry Serum Assay To Quantify M‑Protein in the Presence of Therapeutic Monoclonal Antibodies

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journal contribution
posted on 09.02.2018, 00:00 by Marina Zajec, Joannes F. M. Jacobs, Patricia J. T. A. Groenen, Corrie M. de Kat Angelino, Christoph Stingl, Theo M. Luider, Yolanda B. De Rijke, Martijn M. VanDuijn
M-protein diagnostics can be compromised for patients receiving therapeutic monoclonal antibodies as treatment in multiple myeloma. Conventional techniques are often not able to distinguish between M-proteins and therapeutic monoclonal antibodies administered to the patient. This may prevent correct response assessment and can lead to overtreatment. We have developed a serum-based targeted mass-spectrometry assay to detect M-proteins, even in the presence of three therapeutic monoclonal antibodies (daratumumab, ipilimumab, and nivolumab). This assay can target proteotypic M-protein peptides as well as unique peptides derived from therapeutic monoclonal antibodies. We address the sensitivity in M-protein diagnostics and show that our mass-spectrometry assay is more than two orders of magnitude more sensitive than conventional M-protein diagnostics. The use of stable isotope-labeled peptides allows absolute quantification of the M-protein and increases the potential of assay standardization across multiple laboratories. Finally, we discuss the position of mass-spectrometry assays in monitoring minimal residual disease in multiple myeloma, which is currently dominated by molecular techniques based on plasma cell assessment that requires invasive bone marrow aspirations or biopsies.